Method and composition for chemical polishing

ABSTRACT

A method of polishing a surface such as a surface of a material layer on a substrate is provided. In one embodiment, a substrate having a material layer thereon is provided. The material layer has a surface with a plurality of features having a feature size less than about 1 micron. The surface is contacted with a polishing composition that comprises a compound capable of reacting with the material layer. Relative motion is provided between the polishing composition and the surface to be polished, and portions of the material layer are removed, thereby reducing the feature size of the features on the surface of the material layer. The surface is irradiated with sonic energy. The polishing composition may comprise ozone. In another aspect of the invention, a polishing composition comprising about 1 part per million (ppm) to about 50 ppm of ozone and a sufficient concentration of acid to solubilize the ozone is provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a polishing a surface, and more particularly to polishing the surfaces of layers used in integrated circuits.

[0003] 2. Description of the Related Art

[0004] In the fabrication of integrated circuits, substrate surface planarity is of critical importance. This is especially so as the scale of integration increases and device features are reduced to sub-micron levels. Integrated circuits typically include conductive layers that are used to interconnect individual devices of the integrated circuit. The conductive layers are typically isolated from each other by one or more dielectric layers. Holes (vias) formed through the dielectric layers provide electrical access between successive conductive interconnection layers.

[0005] It is desirable for a conductive metal layer to have a smooth topography to facilitate subsequent process steps performed thereon. For example, it is difficult to control feature sizes in conductive metal layers applied over nonplanar surfaces using conventional photolithography techniques.

[0006] Copper is one material becoming increasingly used in integrated circuits for the metal layers that provide the electrical access between successive interconnection layers. Copper is preferred due to desirable properties such as lower resistance and better electromigration performance compared to traditional materials such as aluminum.

[0007] Copper may be deposited by various techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD) and electrochemical plating (ECP). Copper features are typically formed using a damascene process in which a feature is defined in a dielectric material and subsequently filled with copper. The copper is deposited both in the features and on the surrounding field. The copper deposited on the field is then removed to leave the copper filled feature formed in the dielectric. The copper deposited on the field may be removed using techniques such as chemical mechanical polishing (CMP).

[0008] In CMP, an abrasive polishing slurry may be used in conjunction with mechanical energy to remove material from the substrate surface. However, with the progressive reduction in device dimensions on integrated circuits (ICs), it is challenging for CMP to provide sufficient surface planarity to meet future needs for IC fabrication.

[0009] Therefore, a need exists in the art for a method for polishing a surface, such as the surface of a copper layer, to a high degree of surface planarity.

SUMMARY OF THE INVENTION

[0010] Embodiments of the present invention generally relate to a method of polishing a surface such as a surface of a material layer on a substrate. In one embodiment, a substrate having a material layer thereon is provided. The material layer may be, for example, a copper layer. The material layer has a surface with a plurality of features thereon, and the features have a feature size less than about 1 micron. The surface is contacted with a polishing composition that comprises a compound capable of reacting with the material layer. Relative motion is provided between the polishing composition and the surface to be polished, and portions of the material layer are removed, thereby reducing the feature size of the features on the surface of the material layer.

[0011] In another embodiment, the method comprises providing a material having a surface to be polished. The surface is contacted with a polishing composition, and the surface to be polished is irradiated with sonic energy. Relative motion may be provided between the polishing composition and the surface to be polished during the irradiation of the surface with sonic energy.

[0012] In another embodiment, the method comprises providing a substrate having a material layer thereon, the material layer having a surface to be polished. The surface is contacted with a polishing composition comprising an oxidizing agent such as ozone or oxygen. Relative motion between the polishing composition and the surface to be polished may be provided.

[0013] In another embodiment, the method comprises providing a substrate with a material layer thereon, the material layer having a surface to be polished. The surface is contacted with a polishing composition comprising ozone, and relative motion between the polishing composition and the surface to be polished is provided. The surface is irradiated with sonic energy. The sonic energy may be megasonic energy and may have a frequency in a range of about 400 kilohertz (kHz) to about 9 megahertz (MHz). In one embodiment, the sonic energy has a frequency of about 900 kHz. The surface may be irradiated while the surface is contacted with the polishing composition.

[0014] In another embodiment, the method comprises providing a substrate having a material layer thereon retained in a face-up orientation, wherein the material layer has a surface to be polished. A polishing composition is projected downward onto the surface to be polished. Relative motion is provided between the polishing composition and the surface to be polished, and the surface is irradiated with sonic energy. The sonic energy may be megasonic energy, and may have a frequency in a range of about 400 kHz to about 9 MHz.

[0015] In another aspect of the invention, a polishing composition is provided. In one embodiment, the polishing composition comprises water, about 1 ppm to about 50 ppm of ozone, and a sufficient concentration of acid to solubilize the ozone.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.

[0017] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0018]FIG. 1 is a schematic side view of a polishing apparatus that may be used to practice of embodiments described herein;

[0019]FIG. 2 is a three dimensional perspective view of a bracket that may be used in embodiments of the polishing apparatus described herein;

[0020]FIG. 3 is a close-up cross-sectional view of the polishing apparatus of FIG. 1;

[0021]FIG. 4 is a cross-sectional view of a material layer having a surface that may be polished using embodiments described herein;

[0022]FIG. 5 is a series of method steps for polishing a surface according to embodiments described herein; and

[0023]FIG. 6 is a schematic cross-sectional view of a substrate undergoing a polishing process consistent with embodiments described herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] Embodiments described herein relate to a method for polishing a surface. The surface may be a top surface of a material layer formed on a substrate. A polishing fluid is flowed over the surface while the substrate is moved relative to the polishing fluid. The relative motion may be, for example, rotational motion. FIG. 1 is a schematic side view of a polishing apparatus 2 that may be used to polish the surface as described herein. The polishing apparatus 2 includes a chamber 29 for processing a substrate 30.

[0025] The substrate 30 is supported above a disc or platter 22 by a rotatable bracket 32 that positions the substrate 30 substantially parallel to the top surface 24 and the bottom surface 26 of the platter 22. The bracket 32 has a size and shape that accomodates the substrate 30 having a top surface 42 to be polished and a bottom surface 122. The platter 22 may have a diameter that is typically at least as great as the diameter of the substrate 30.

[0026] Positioned beneath the platter 22 is a motor 36 that rotates a shaft 20 that is coupled to the bracket 32 about an axis 92. A cavity 34 within the shaft 20 serves as a conduit for electrical connectors that are coupled to an array of transducers 28 as well as a tube 90 for supplying a backside fluid to a port 38. Backside fluid flowing through the port 38 flows onto the top surface 24 of the platter 22 and onto the bottom surface 122 of the substrate 30.

[0027] The platter 28 is constructed of material that is compatible with the fluids used during the polishing process. The platter 22 may comprise, for example, stainless steel, aluminum, silicon carbide, among other materials. The top surface 24 of the platter 22 may be polished such that the top surface has a surface variation of about 16 rms (0.4 microns).

[0028] A coating (not shown in FIG. 1) may be formed on the top surface 24 of the platter 22 to provide enhanced chemical resistance to the platter 22. The coating may comprise, for example, a polymeric material such as polytetrafluoroethylene material (e.g. Teflon® available from E. I. du Pont de Nemours and Company of Wilmington, Del.) or an polychlorotrifluoroethylene material (e.g Halar®) available from Ausimont USA of Thorofare, N.J.). The coating may be designed to provide a high degree of resistance to a strong oxidizing agent, such as ozone (O₃).

[0029]FIG. 2 is a three dimensional perspective view of a bracket that may be used in embodiments of the polishing apparatus described herein. The substrate 30 may be held in place by the bracket 32 to position the substrate 30 parallel to and proximate to the platter (not shown in FIG. 2). The bracket 32 may hold the substrate 30 by gravity at contact points 209 (four are shown by way of example) along the edge 215 of the substrate 30 such that the substrate 30 is clear of the bracket 32 structure and fully exposed to fluids that may be applied to the top surface 42 and the bottom surface 122 of the substrate 30. The contact points 209 may be positioned at the end of bracket support posts 211. The contact points 209 may comprise, for example, an elastomeric material to friction grip the substrate 30.

[0030]FIG. 3 depicts a close-up, cross-sectional view of the platter 22 having bottom surface 26 with the array of transducers 28 thereon. The transducers 28 are arranged along the bottom surface 26 of the platter 22 such that the combined area of the transducers 28 generally provides between about 70 % and about 100% area coverage of the bottom surface 26 of the platter 22. The transducers 28 may be arranged in a single strip along a diameter of the bottom surface 26 of the platter 22 providing a coverage of between about 10% and about 60% area coverage of the bottom surface 26 of the platter 22. Alternatively, a greater density of transducers 28 may be placed on the bottom surface 26 of the platter 22, such that the transducers 28 cover between about 70% and about 100% area coverage of the bottom surface 26.

[0031] The transducers 28 may be of any shape such as circular, hexagonal, square, etc. in order to provide adequate coverage of the bottom surface 26 of the platter 22. A metal spring 50 may be attached to each transducer 28 such that the transducer 28 maintains contact with the platter 22. The spring 50 may be, for example, a coiled wire, and is shaped to maintain electrical contact with the transducer 28. Electrical leads 52 are coupled to the springs 50 to electrically connect the springs 50 and the transducers 28 to a high frequency power source 54.

[0032] The transducers 28 comprise a piezoelectric material, such as, for example, lead zirconate titanate (PZT) among other piezoelectric materials. The transducers 28 are sized to generate acoustic waves at a particular frequency in response to an applied high frequency power. The transducers 28 are capable of emitting sonic radiation. The sonic energy may be megasonic energy, having a frequency that may be in a range of about 400 kHz to about 9 MHz. In one embodiment, the sonic energy has a frequency of about 900 kHz. The sonic energy may have a power density in a range of about 0.1 watts per square centimeter and 10 watts per square centimeter.

[0033] The top surface 24 of the platter 22 may have a coating 110 formed thereon. The coating has a top surface 120. The transducers 28, the platter 22, and the coating 110 each have respective thicknesses 112, 114, 116. The thickness 112 of the transducers, the thickness 114 of the platter 114, and the thickness 116 of the coating, as well as a separation 118 between the top surface 120 of the coating 110 and the bottom surface 122 of the substrate 30 are variable and are selected depending upon the particular wavelength of radiation emitted by the transducers 28 in order to minimize reflections of the sonic energy.

[0034] The thickness of the platter 114, and the thickness 116 of the coating, as well as a separation 118 between the top surface 120 of the coating 110 and the bottom surface 122 of the substrate 30 may be each selected so as to be a multiple of λ/2, where λ is the wavelength of the incident sonic radiation. Alternatively, one or more of the thicknesses including the thickness of the platter 114, and the thickness 116 of the coating, as well as a separation 118 between the top surface 120 of the coating 110 and the bottom surface 122 of the substrate 30 have a thickness that is much smaller than λ/2.

[0035] Alternatively, reflections may be reduced or eliminated by using pulses of sonic energy rather than continuous sonic radiation. The pulses may have a pulsing frequency less than 2L/c, where c is the velocity of the acoustic radiation in the medium, and L is the thickness of the medium.

[0036] In an exemplary embodiment of the invention, the transducers 28 have a thickness 112 of about 0.0982 inches to about 0.0986 inches. The transducers emit pulsed or continuous megasonic radiation having a frequency of about 900 megahertz (MHz). The platter 22 is an aluminum platter having a thickness 114 of about 0.127 inches to about 0.143 inches. The coating 110 comprises a polychlorotrifluoroethylene material and has a thickness 116 in a range of about of about 0.025 inches to about 0.035 inches. The separation 118 between the top surface 120 of the coating 110 and a bottom surface 122 of the substrate 30 may less than about 0.2 inches.

[0037] In another exemplary embodiment, of the invention, the transducers 28 have a thickness 112 of about 0.0984 inches and emit pulsed or continuous megasonic radiation having a frequency of about 900 megahertz (MHz). The platter 22 is an aluminum platter having a thickness 114 of about 0.135 inches. The coating 110 comprises a polychlorotrifluoroethylene material has a thickness 116 of about 0.030 inches.

[0038] The transducers 28 may be attached to the bottom surface 26 of the platter 22 using, for example, an adhesive that is compatible with the backside fluid, described below. The adhesive may comprise, for example, an electrically conductive epoxy or solder having a thickness of about 0.001 inches to about 0.01 inches.

[0039] Referring again to FIG. 1, a spray device or nozzle 40 is positioned above the substrate 30. The nozzle 40 provides a polishing fluid or composition to the top surface 42 of the substrate 30. The nozzle 40 is coupled to a polishing composition supply line 44, which is in turn connected to one or more polishing fluid supply tanks 46, 48 (two are shown by way of example in FIG. 1). Valves 12 and 52, such as mechanical or electronically controlled valves 12, 52 permit the one or more polishing fluids to flow from the supply tanks 46, 48 through the supply line 44 to the nozzle 40. While one nozzle is depicted in FIG. 1, alternatively, a plurality of nozzles 40 may be positioned to provide polishing composition to the substrate 30.

[0040] The nozzle is designed such that it supplies polishing composition at a sufficiently high rate such that the top surface 42 of the substrate 30 is coated with a continuous film of polishing fluid. The thickness of the film of polishing fluid is greater than a depth or size of features on the substrate 30 that are to be polished.

[0041] The polishing apparatus 2 may further comprise a housing 4 that protects the substrate 30 from stray particles including dust and other contaminants that might otherwise adversely impact the polishing process. An optional filtration device 6 includes a series of filters 8 such as, for example, ultra low penetrating air (ULPA) filters to filter an interior processing area 9. The ULPA filters are capable of filtering out particles and other contaminants having a particle size greater than about 0.1 microns. The apparatus may comprise a drain 18 to capture spent fluids from the polishing process.

[0042] The above description with reference to FIGS. 1-3 depict the apparatus 2 in which the substrate 30 has a top surface 42 to be polished that is oriented up (i.e. a face-up orientation). The nozzle 40 is positioned above substrate 30 and the transducers 28 positioned below the substrate 30. Other configurations of the substrate 30, the nozzle 40 and the transducers 28 are within the scope of the invention. In one alternative embodiment of the invention, the substrate 30 is oriented such that the surface 42 to be polished is positioned face down such that the material layer 310 to be polished contacts a polishing composition. The polishing composition and the substrate 30 may be rotated with respect to one another. In another alternative embodiment of the invention, the transducers 28 are positioned above the substrate 30.

[0043] Other aspects of the apparatus 2 that may be used to practice embodiments described herein include those detailed in “Method and Apparatus for Wafer Cleaning,” U.S. patent application, Ser. No. 09/603,792, filed Jun. 25, 2001, which is incorporated herein by reference in its entirety.

POLISHING METHOD

[0044]FIG. 4 shows a cross-sectional view of substrate 300 having a top surface 302 and a bottom surface 304. The material layer 310 is formed on the top surface 302 of the substrate 300. The material layer 310 has a bottom surface 314 and an irregular top surface 312 with peaks 316 and valleys 318. The peaks 316 have a peak height 320 and the valleys have a valley height 322. A feature size 324 (i.e., a difference between the peak height 320 and the valley height 322) may be less than about 1 micron.

[0045]FIG. 5 depicts a series of method steps 400 for polishing the top surface 312 of the material layer 310. The series of method steps 400 begins at step 402 in which the material layer 310 having a plurality of features thereon is provided. The material layer 310 may be formed on the substrate 300, which is placed into, for example the bracket 32 of the apparatus 2 detailed in FIG. 1. The bracket 32 may be lowered to align the substrate 300 a predetermined distance from the platter 30. The material layer 310 may comprise a conductive or metallic material, such as, for example copper (Cu), aluminum (Al), or tungsten (W). The material layer 310 may comprise other materials to be polished.

[0046] As indicated in step 404, the top surface 312 of the material layer 310 is contacted with a polishing composition. The polishing composition generally comprises one or more reactants that are capable of chemically reacting with the material layer 310 and rendering the material layer 310 soluble in the polishing composition. The reactants may include an oxidizing agent, such as, for example, ozone (O₃), oxygen (O₂), a peroxide compound, among other oxidizing compounds. The reactants may include an acidic compound such as, for example acetic acid, hydrochloric acid, among other acids. The reactive compounds may also include a complexing agent, such as, for example, an amine compound that sequesters or forms soluble complexes with the material layer 310. Various reactants such as oxidizing compounds, acidic compounds, and complexing agents may be used in combination to enhance the ability of the polishing composition to react with the material layer 310.

[0047] The polishing composition may further comprise a stabilizing compound that provides shelf stability to, for example, the oxidizing agent. The stabilizing compound may, for example, reduce the rate of chemical reactions within the polishing composition that would adulterate the polishing composition before it is used to polish a material layer. The polishing composition may further comprise a solubility modifying compound that serves to increase the solubility of one or more reactants within the polishing composition. The solubility modifying compound may be, for example, an acidic compound, such as acetic acid, hydrochloric acid, etc. The polishing composition may comprise other ingredients known to the art of polishing material layers for integrated circuit applications, such as, for example, corrosion inhibitors, wetting agents, or buffers.

[0048] The polishing composition typically comprises a solvent such as deionized water, useful for carrying or transporting the above-mentioned compounds to the top surface 312 of the material layer 310. In one embodiment, the polishing composition comprises an oxidizing agent such as ozone (O₃). The ozone may have a weight concentration in a range of about 1 ppm to about 50 ppm. The ozone-based polishing composition may further comprise an acidic stabilizing compound in a concentration by weight in a range of about 5% to about 100%. The acidic stabilizing compound may be, for example, acetic acid. In one embodiment, the ozone-based polishing composition has a concentration of acetic acid of about 30% by weight. The ozone-based polishing composition may further comprise deionized water.

[0049] The acidic stabilizing compound increases the concentration of ozone that may used in the polishing composition by increasing the solubility of ozone in the polishing composition. The acidic stabilizing compound may also enhance the polishing rate of the material layer 310. The ozone-based polishing composition preferably does not comprise any ingredients that would de-stabilize, pre-maturely react with, or degrade the ozone in the polishing composition.

[0050] Alternatively or in addition to ozone, the polishing composition may comprise other oxidizing agents such as oxygen. The oxygen may be added to the polishing composition by, for example, bubbling air or purified oxygen into the polishing composition. The concentration of oxygen in the polishing composition may be high enough such that the polishing composition is saturated with dissolved air or dissolved oxygen for the specific composition, temperature, and pressure of the polishing composition. The concentration of oxygen in the polishing composition may be, for example, in the range of about 7 parts per million (ppm) to about 10 ppm. In addition to oxygen, the polishing composition may further comprise an acidic compound, such as, for example sulfuric acid. The acidic compound may be present in a concentration such that the pH of the polishing composition is in the range of about 0 to about 4. The acidic material generally functions to improve the polishing rate of the polishing composition and may stabilize the oxygen within the polishing composition such that the oxygen remains dissolved within the polishing composition.

[0051] The above-described polishing composition comprising an oxidizing agent is particularly useful for polishing copper surfaces. The polishing composition may be provided to the top surface 312 of the material layer 310 using a nozzle applicator such as nozzle 40 of FIG. 1. The pressure of the polishing fluid exiting the nozzle may be in the range of about 3 psi to about 20 psi. The polishing composition flows onto the substrate 300 at a flow rate that is fast enough such that the polishing composition forms a continuous film on the top surface 310 of the material layer 312. The flow rate may be in a range of about 0.1 liters per minute to about 4 liters per minute.

[0052] Referring to step 406 of FIG. 5, relative motion between the substrate 300 and the polishing fluid may be provided. The relative motion may be provided by placing the substrate 300 into a polishing apparatus such as the polishing apparatus 2 of FIG. 1. The substrate 300 may be loaded into the chamber 29 and positioned on the bracket 32. The bracket 32 and the substrate 300 held thereon rotate with respect to the polishing composition.

[0053] Referring to FIGS. 1-3, a backside fluid may be provided to the top surface 24 of the platter 22 such that the backside fluid completely fills the separation 118 between the top surface 120 of the coating 110 and the bottom surface 304 of the substrate 300. For embodiments in which no coating 110 is formed on the top surface 26 of the platter 22, the backside fluid may completely fill the separation 118 between the top surface 120 of the platter 26 and the bottom surface 304 of the substrate 300. The backside fluid generally provides a consistent fluid medium between the platter 22 and the substrate 300 in order to reduce undesirable reflections of megasonic energy. The backside fluid generally does not contact the material layer 310 formed on the top surface 302 of the substrate 300 due to rotation of the substrate 300. The backside fluid may comprise, for example, deionized water.

[0054]FIG. 6 is a schematic cross-sectional view of a substrate 300 undergoing a polishing process consistent with embodiments described herein. The relative motion between the substrate 300 and the polishing composition results in the formation of a film 530 in contact with the top surface 312 of the material layer 310. The film may have a thickness of at least about 100 microns. The film 530 is characterized as having a slow moving boundary layer 540 adjacent to the top surface 312 of the material layer 310. The boundary layer 540 has a thickness 550 which depends upon the relative motion between the substrate 300 and the polishing composition (e.g. speed of rotation), the composition and viscosity of the polishing composition, the feature size of the top surface 312 of the material layer 310, as well as the geometry of the substrate 300. In general these variables are selected such that the boundary layer 540 has a thickness 550 that is on the same order of magnitude as the feature size 324 of the material layer 310. The thickness 550 of the boundary layer 540 may be less than about ten times the feature size 324 of the top surface 312 of the material layer 310. In general, the speed of rotation may be greater than about 2 rpm.

[0055] It is believed that reactants in the polishing composition adjacent to the material layer 310 preferentially react with the material layer 310 at the top of the peaks 316 rather than the material layer at the bottom the valleys 318. It is further believed that if the polishing composition comprises a compound that is highly reactive with the material layer 310, the boundary layer 540 thereby established, is a zone in which the rate of removal of material from the material layer 310 is limited by the time required to transport material from the top surface 312 of the material layer 310, across the boundary layer 540 rather than by the time required for components of the polishing composition to react with the material layer 310. This “diffusion-limited” property is useful in that peaks 316 react faster with the polishing composition than valleys 318, resulting in smoothening or polishing of the top surface 312 of the material layer 310. The feature size 324 is thereby reduced.

[0056] Referring to step 408 of FIG. 5, the top surface 312 of the material layer 310 may be irradiated with sonic energy. The sonic energy may be megasonic energy having a frequency of at least about 900 kHz. The megasonic energy may be a range of about 400 kHz to about 9 MHz. The sonic energy may provided to the top surface 312 of the material layer 310 by positioning the array of transducers 28 proximate (e.g. below) the substrate 300, for example, as depicted in FIG. 1. The sonic radiation may travel through one or more media before interacting with the top surface 312 of the material layer 310. For example, the sonic radiation may travel through the platter 22, through the coating 110, across a separation 118 between the top surface 120 of the coating 110 and a bottom surface 304 of the substrate 300, through the bottom surface 304 of the substrate 300, through the substrate 300, and into the polishing composition that is in contact with the top surface 312 of the material layer 310. Alternatively, the array of transducers 28 may be positioned above the substrate 300 such that the megasonic radiation impinges upon the top surface 512 of the material layer 310 without having to travel through the substrate 300. The sonic radiation may be incident to the substrate 300 at an angle substantially normal to the top surface 302 of the wafer 300.

[0057] The sonic radiation is believed to reduce the thickness 550 of the boundary layer 540 through one or more mechanisms. For example, it is believed that the megasonic radiation reduces the thickness 530 of the boundary layer 540 by a cavitation process. Small and controlled bubbles formed by the interaction of the radiation with the polishing composition impinge upon and disrupt the slow moving boundary layer 540.

[0058] By using the sonic radiation to reduce the thickness 550 of the boundary layer 540, it is possible to use lower rotation speeds and still achieve a boundary layer 540 that has a thickness 550 that is small enough to reduce the feature size of features that are less than about 1 micron.

[0059] Referring again to FIG. 5, the method ends with step 410. While FIG. 5 depicts a series 400 of method steps beginning with step 402 and ending with step 410, the contacting of the top surface 310 of the material layer 312 (step 404), the relative motion provided between the polishing composition and the top surface 310 of the material layer 312 (step 406) and the irradiation of the top surface 310 of the material layer 312 (step 408) generally overlap in time. In other words, the top surface 310 of the material layer 312 is generally contacted with the polishing composition (step 404) during the period in which relative motion is provided between the polishing composition and the top surface 310 of the material layer 312 (step 406). For embodiments in which the top surface 310 of the material layer 312 is irradiated with megasonic energy, irradiation (step 408) generally takes place during a period in which relative motion is provided between the polishing composition and the top surface 310 of the material layer 312 (step 406).

[0060] While the method described above is presented as a method of polishing of material layers, such as conductive layers formed on a substrate, the scope of the present invention is not limited thereto. For example, embodiments of the invention described herein may be used to polish the surface of a substrate such as a silicon wafer substrate. The silicon substrate to be polished may have features having a feature size less than about one micron. The silicon surface is contacted with a polishing composition, and the silicon surface to be polished is irradiated with sonic energy. Relative motion may be provided between the polishing composition and the silicon surface to be polished during the irradiation of the silicon surface with sonic energy. The polishing composition may comprise an oxidizing agent such as ozone or oxygen.

[0061] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

1. A method of polishing, comprising: irradiating a surface of a material to be polished with sonic energy; and contacting the surface with a polishing composition.
 2. The method of claim 1 wherein the contacting of the surface with the polishing composition is performed during the irradiation of the surface.
 3. A method of polishing, comprising: contacting a surface of a material layer formed on a substrate with a polishing composition, wherein the polishing composition comprises a reactant capable of reacting with the material layer, and wherein the surface of the material layer has a plurality of features having a feature size less than about 1 micron; providing relative motion between the polishing composition and the surface; and removing portions of the material layer to reduce the feature size of the features, while irradiating the surface with sonic energy.
 4. A method of polishing, comprising: contacting a surface of a material layer formed on a substrate with a polishing composition comprising ozone; and polishing the material layer.
 5. The method of claim 4 further comprising providing relative motion between the polishing composition and the surface.
 6. A method of polishing, comprising: contacting a surface of a material layer with a polishing composition comprising an oxidizing agent; and providing relative motion between the polishing composition and the surface, while irradiating the surface with sonic energy.
 7. The method of claim 6 wherein the sonic energy has a frequency in a range of about 400 kilohertz (kHz) to about 9 megahertz (9 MHz).
 8. The method of claim 6 wherein the oxidizing agent is selected from the group consisting of ozone, oxygen, and combinations thereof.
 9. A method of polishing, comprising: retaining a substrate having a material layer thereon in a face-up orientation, wherein the material layer has a surface to be polished; projecting a polishing composition downward onto the surface to be polished; providing relative motion between the polishing composition and the surface to be polished; and irradiating the surface with sonic energy.
 10. The method of claim 9 wherein the polishing composition is projected onto surface to be polished at a rate sufficient to form a continuous film of polishing composition on the surface of the material layer.
 11. A polishing composition, comprising: about 1 part per million (ppm) to about 50 ppm ozone; and a sufficient concentration of acid to solubilize the ozone.
 12. The polishing composition of claim 11 wherein the concentration of acid is in a range of about 5% by weight to about 100% by weight. 